When the Pilgrims landed on the shores of what is now Cape Cod in late November of 1620, they “fell upon their knees and blessed the God of Heaven” for delivering them to a safe harbor. It had been a harrowing two month-long voyage from England on the Mayflower, but their troubles were far from over.

The Pilgrims of Plymouth Colony struggled greatly that first winter, with half of the Mayflower’s passengers dying of tuberculosis and pneumonia before spring arrived. Yet by the autumn of 1621—exactly 400 years ago—their situation had improved. This was largely thanks to help from the neighboring Wampanoag people and particularly the now-famous Tisquantum, or Squanto. Sometime that autumn, the colonists enjoyed a three-day feast with the Wampanoag chief Massasoit (also known as Ousamequin) and 90 of his men who came to Plymouth. This year marks the 400th anniversary of that feast, which would later be considered the mythical origin of the Thanksgiving holiday we celebrate today.

But we must place the “First Thanksgiving” into its proper historical context: one of brutal violence under colonialism. While the legend describes how two cultures came together peacefully to enjoy a meal, the reality was likely rather different. The feast was almost certainly a tense political moment, not a carefree celebration of cross-cultural understanding. After all, 90 Wampanoag warriors showed up at Plymouth, likely unannounced. In contrast, fewer than 50 Pilgrims had survived that first winter. The English and the local tribes were highly suspicious of one another, and violence between them would become increasingly common in subsequent years.

Thanksgiving celebrations were regular occurrences in colonial North America, with some commemorating the sort of colonial violence that would become commonplace. While not the inspiration for the Thanksgiving holiday we now celebrate, one such day of thanksgiving was announced in the Massachusetts Bay Colony in 1637 to celebrate the event now known as the Mystic Massacre. In 1637, during the Pequot War, a contingent of English soldiers and their Native allies surrounded and burned a Pequot village near present-day Mystic, Conn. The several hundred Pequot men, women and children inside the fortified village were all killed or burned alive. The English saw this event as divine justice against the Pequot “wrought so wonderfully” by God, and the governor of the Massachusetts Bay Colony declared a day of thanksgiving in response.

In addition to its historical context of colonial conflict, the First Thanksgiving must also be put into its ecological context. The Pilgrims wrote that the feast in the autumn of 1621 was to give thanks to God for leading them to a place where they had “all things in good plenty.” After the harvest of corn was brought in, a group of Wampanoag men went out and returned with five deer, and four Englishmen killed enough waterfowl to last the colony a week, while others hunted turkeys.

The ease at which the Pilgrims and Wampanoag were able to harvest and hunt speaks to the existence of the highly productive environment that the Pilgrims were celebrating. But why was the land around Plymouth so productive? Why was the soil so fertile, and why were plant and animal resources so abundant there?

While the Pilgrims thanked their God for the natural abundance of their new home, they should have been thanking the Native American inhabitants of the region. The land around Plymouth Colony was likely so productive due to thousands of years of modification and management by Native peoples, who had created a symbiotic network of connections between people, plants, and other animals.

It is a mistake to imagine the landscape of North America as a pristine and untouched wilderness prior to the arrival of Europeans. Archaeologists, historians, and environmental scientists have long recognized that Native peoples actively managed their environments—and of course Native peoples themselves have long said this was the case. The Pilgrims landed in a region of North America that had been tended to by its Native inhabitants for generations. The land around Plymouth was so productive because in fact, Plymouth was built directly on the village of Patuxet, a Native American settlement that had been abandoned not long before because of an epidemic disease outbreak. Squanto was said to have been the last surviving Patuxet as he had been kidnapped and sold into slavery in Europe in 1614, thereby avoiding the disease outbreak that killed the rest of his tribe. The Pilgrims therefore enjoyed the benefits of living in an area which had been, until recently, a site of likely substantial ecosystem engineering by the Patuxet.

This ecosystem engineering mostly took the form of controlled burns. In New England, historical accounts from the 17th century describe how the local Native peoples would deliberately set fires in the forests every autumn. Not only was fire used to prepare fields for planting corn, beans and squash, but it was also used to clear away underbrush while maintaining the forest canopy. This facilitated travel and hunting in addition to rejuvenating the ecosystem. Such burning likely resulted in a patchwork mosaic of fields and forests, with the forests close to where Native people lived often lacking any understory vegetation. English colonists arriving in the region described exactly this sort of landscape, noting that the only places with dense vegetation were those in which the local tribes were devastated by disease and could no longer tend the forests.

Forest management through fire would have likely created a very productive ecosystem capable of providing abundant food and other resources to the people living there. In the wake of fires, soils were rejuvenated with nutrients, and lush new-growth vegetation supplied food to herbivores, which in turn supplied food to carnivores. Native peoples could harvest the strawberries and blackberries growing in recently burned fields as well as the game animals attracted to these same areas.

Of these game animals, white-tailed deer may have been the most important. Deer were the chief prey of Native Americans in the region and featured prominently on the menu at the First Thanksgiving. They love exactly the sort of ecological disturbance created by Native fires and forest clearing. As many present-day residents of eastern North America can attest, deer are quite common in backyards, parks, highway corridors and on farms. This is because the species isn’t actually adapted to deep and dense forests, but to forest edges. Deer thrive at the boundaries of forests and fields—especially agricultural fields—and this is exactly the sort of habitat that would have been created by Native American burning across eastern North America before Europeans arrived. White-tailed deer appear to have remained quite numerous prior to European colonization, even though they were regularly hunted by Native peoples.

After millennia of ostensibly sustainable hunting by Native peoples, evidence suggests that New England’s deer population crashed within a few years of European colonization.

Evidence for such a population crash can be found in the legal codes of the early colonies. In the mid-17th century, the colonies of southern New England began restricting deer hunting to only certain months of the year in an attempt to curtail overhunting. Portsmouth, R.I., became the first in 1646, instituting a closed hunting season for deer from May through October, but many other colonies followed suit in the latter 17th and early 18th centuries.

Around the time that these colonies were beginning to prohibit deer hunting out of season, the Dutch colonist Adriaen Van Der Donck was told by Native interlocutors in the New York area that “before the arrival of the Christians, many more deer were killed than there are now, without any perceptible decrease of their numbers.” If Native hunters were indeed killing more deer in the past than even existed by the mid-17th century, deer populations must indeed have been high prior to European colonization.

What all of this means is that when the Pilgrims landed in 1620, prior to the widespread arrival of European colonists, much of the ecology of New England would have likely still been managed by Native Americans. Controlled burns were common, and disturbance-loving animals like deer were abundant. When the Pilgrims planted their fields and hunted game, they were enjoying the ecological legacy of what Native American environmental managers had engineered over the course of thousands of years before Europeans set foot in North America.

Another factor contributed to the ecology that Pilgrims encountered: epidemic disease.

An outbreak of an unknown disease likely transmitted by European fishermen occurred between 1616 and 1618 in coastal areas of New England. This epidemic led to severe mortality in many coastal Native communities. The English colonists interpreted this disease outbreak as the will of God, and praised him for clearing a path for them to settle New England by killing off many of the Native inhabitants. The epidemic was disastrous. Native people died in droves, and their remains were said to have been left unburied as the few survivors could not feasibly do anything given the scale of the carnage. English colonist Thomas Morton wrote that even several years after the disease outbreak, “the bones and skulls … made such a spectacle … that as I [traveled] in that forest near the Massachusetts, it seemed to me a new found Golgotha,” in reference to the skull-shaped hill outside of Jerusalem where Jesus is said to have been crucified.

It was this epidemic that wiped out the Patuxet tribe and allowed the Pilgrims to enjoy the ecological benefits of living on Patuxet land with no Patuxet remaining, save for Squanto.

Archaeologists have found that deer populations in California and the American Southwest increased after epidemic disease devastated Native communities in those regions. It is therefore possible that immediately after coastal New England was largely depopulated in 1616–1618, deer and other species may have increased in number simply because no one was left to hunt them. This could explain some of the environmental abundance enjoyed by the Pilgrims upon their arrival in 1620, though it may be just as likely that the loss of Native environmental managers might actually have reduced deer populations given the mutualistic symbiosis between them. There is currently no clear evidence for environmental rebound in New England, but it may have occurred on a smaller scale that has yet to be widely perceived by archaeologists and ecologists.

It seems likely that the ecological abundance enjoyed by the Pilgrims four centuries ago during the First Thanksgiving was the result of deliberate and skillful environmental management by Native peoples. Beyond the help of Native individuals like Squanto, the land itself aided the Pilgrims. After all, it had been engineered by Native Americans to be productive. The lesson from this should be clear. It is possible for humans to actively coexist with their environments in ecologically sustainable ways, and we would do well to reflect on how that can best be accomplished today.